Various package-structure type semiconductor devices have been proposed and brought to the commercial stage as semiconductor devices each of which seals a semiconductor chip with a resin encapsulater. For instance, Unexamined Patent Publication No. Hei 11(1999)-330343 discloses a semiconductor device called a “QFN (Quad Flatpack Non-Leaded Package) type”. Since the QFN type semiconductor device takes a package structure wherein electrode members (leads) electrically connected to their corresponding electrodes of a semiconductor chip are exposed from a mounting surface of a resin encapsulater, the semiconductor device can be reduced in planar size as compared with a semiconductor device called a “package structure, e.g., a QFP (Quad Flatpack Package) type” wherein leads electrically connected to electrodes of a semiconductor chip protrude from sides of a resin encapsulater.
The QFN type semiconductor device is manufactured according to an assembly process using a lead frame. When it is of a package structure wherein a semiconductor chip is placed on a die pad, for example, a die pad (also called a tub) formed integrally with a frame main body (frame body) of a lead frame through suspension leads is principally loaded with a semiconductor chip. Thereafter, electrodes (bonding pads) of the semiconductor chip, and electrode members formed integrally with the frame body of the lead frame are electrically connected to one another by bonding wires. Afterwards, the semiconductor chip, the electrode members, the die pad, the suspension leads and the bonding wires, etc. are sealed with a resin encapsulater. Subsequently, the electrode members and the suspension leads are cut and separated from the frame body of the lead frame, whereby the semiconductor device is fabricated. One ends of the bonding wires are connected to their corresponding electrodes of the semiconductor chip, whereas each of the other ends thereof is connected to its corresponding internal connecting surface (one main surface) of both the internal connecting surface and an external connecting surface (other main surface) opposite to each other, of each electrode member. The external connecting surfaces of the electrode members are exposed from a mounting surface of both an upper surface (one main surface) and the mounting surface (other main surface) opposite to each other, of the resin encapsulater.
The resin encapsulater of the QFN type semiconductor device is formed by a transfer molding method suitable for mass production. The formation of the resin encapsulater by the transfer molding method is carried out as follows: A lead frame is positioned between an upper mold and a lower mold of a molding die so that a semiconductor chip, electrode members, a die pad, suspension leads and bonding wires, etc. are located inside a cavity defined by the upper and lower molds thereof. Thereafter, a resin is injected under pressure into the cavity defined in the molding die, whereby the corresponding resin encapsulater is formed.
While the package structure wherein the external connecting surfaces of the electrode members are exposed from the mounting surface of the resin encapsulater, is obtained by positioning the lead frame to the molding die so that the electrode members contact the lower mold of the molding die and thereafter injecting the resin into the cavity of the molding die under pressure. In this case, however, the package structure is easy to cause a problem in that since the adhesion between the lower mold and each electrode member inside the cavity is low, the resin is apt to enter between the lower mold and the electrode member, and the mounting surface of each electrode member is covered with a thin-film unnecessary resin body (resin burrs).
Thus, the technology (hereinafter “sheet mold technology”) of interposing a resin sheet (resin film) between the lower mold of the molding die and the lead frame, positioning the lead frame to the molding die so that the resin sheet makes contact with each electrode member, and thereafter injecting the resin into the cavity of the molding die under pressure has generally been adopted upon the manufacture of the QFN type semiconductor device. Since the adhesion between the resin sheet and each electrode member lying inside the cavity is high in the case of the present sheet mold technology, the sheet mold technology is capable of restraining the occurrence of the problem that the mounting surface of each electrode member is covered with the resin burrs. The sheet mold technology has been disclosed in Unexamined Patent Publication No. Hei 11(1999)-274195, for example.